(1) insultive
(2) pure exclamation
(3) adjective meaning the best
(4) term of affection
(5) can be defined with 'ma niz' to make a general exclamation, usually used to express outrage, agner or enthusiasm

(1) what did you do that for you shiz?
(2) shiz! that was amazing
(3) that was the shiz
(4) hey shiz! (as in hey chick, hey girlfriend etc)
(5) shiz ma niz!

or, alternatively, make up your own definition - its one of those words that can be placed anywhere...